Norwegian version of this page

Functional anatomy of the small pelvic and hip muscles (completed)

The deep gluteal muscles or external hip rotators are known contributors to low back, pelvic and hip pain, but our knowledge about their function and accessibility for exercise is insufficient.

Photo: Jan Ringheim,

To establish an empiric foundation for specific physical actions, we will map the movement range of the deep gluteal muscles in donated human bodies.

About the project

To develop an evidence based understanding of the function of the small and deep pelvic muscles, we will measure changes in muscle length by different rotations of the hip joint. Knowledge on the muscles’ movement range is needed for defining effective physical tests and exercises.

In addition, this knowledge can increase diagnostic understanding of activities that may evoke pain from these muscles, for the benefit for patients groups with low back, pelvic and hip pain.


Our objective is to develop knowledge about optimal positions for stretching and developing strength from the muscles piriformis, obturator internus and gemellii, quadratus femoris, and obturator externus.

Figure: The deep gluteal (external rotator) muscles on posterior and lateral side of the pelvic and hip area. The superficial muscles gluteus maximus (1) and gluteus medius (2) are excised, to uncover the deep sacrospinosus (3) and sacrotuberalis (4) ligaments and the deep gluteal muscles. (Reproduced from with A. Neumann, Kinesiology of the Musculoskeletal System – Foundations for Rehabilitation, 2nd edition, Chapter 12 Hip, p. 496, Elsevier (2010), with permission).


Pain and disability related to the low back, pelvis, and hip is common. A known alternative diagnosis for joint pain is the piriformis syndrome. Piriformis is a deep gluteal muscle which spans the pelvic and hip joint, and which clinically is associated with several diagnoses and symptoms. Lately another deep pelvic and hip muscle, obturator internus, is proposed as the main obstructer of the sciatic nerve.

The function of the deep pelvic and hip muscles, also called external rotators of the hip, is mainly assessed on human bodies with the hip in a straight position. Only one (unpublished) study on human bodies has empirically assessed the function of these muscles in other positions and found evidence indicating other main functions than external rotation of the hip.

However, exercises for stretching and strengthening of the deep gluteal muscles are still performed with straight hips and with main focus on the external rotator function.

We therefore aim to map out the movement range of the deep pelvic and hip muscles, for establishing an empiric foundation for improved physical actions for patients with low back, pelvic, and hip pain.


  • The Establishment Foundation for Advancement of Sports Medicine and Sports Physiotherapy in Norway
  • The Norwegian Fund for Post-Graduate Training in Physiotherapy


Knut Rekdahl, Mechanical Workshop, Institute of Basic Medical Sciences, UiO.


  • Pelvic-hip-specimen will be mounted in a custom made apparatus fixating the pelvic and allowing static positioning of the hip joint in three planes.
  • Muscle lengths will be measured outside the femoral bone by a digital caliper. That is, on non-elastic strings anchored at muscle origins and pulled through muscles and through holes in tendons and bones.
  • Hip positions or joint angles will be decided by an Inertial and Magnetic Measurement System (IMMS, by Xsens). Estimating of the joint angles will be done by an angle dial fixed on the custom-made apparatus and by a hand-held goniometer.


Vaarbakken K, Steen H, Samuelsen G, Dahl HA, Leergaard TB, Nordsletten L, Stuge B. Lengths of the external hip rotators in mobilized cadavers indicate the quadriceps coxae as a primary abductor and extensor of the flexed hip. Clin Biomech (2014), DOI 10.1016/j.clinbiomech.2014.05.011 (In press)

Start - finish

March 2011 - May 2013

Published Mar. 28, 2012 9:34 AM - Last modified Oct. 26, 2015 10:20 AM


Visiting address:

Department of Anatomy
Domus Medica
Sognsvannsveien 9
0372 Oslo

Project leader

Kjartan Vårbakken